There is a solution, described in documents EP1752852B1, EP2778546A1, U.S. Pat. No. 5,443,207A, U.S. Pat. No. 5,622,221A, U.S. Pat. No. 4,629,116, US20100163221, U.S. Pat. No. 7,648,347B2, where there is a pump connected to a heat exchanger. A liquid mass flow through the pump is controlled directly by a temperature difference between either a heat-transfer liquid temperature or a thermal zone temperature and their respective setpoints. This solution uses only one temperature—the heat-transfer liquid of the thermal zone temperature. A disadvantage of this solution is the fact that a power output of the heat exchanger is not independent of inlet stream temperature changes. This solution does not yield a heat delivery control independent of temperature changes on the heat-transport liquid entering a heat exchanger.
An actual absolute heat exchanger power (a heat flow between primary and secondary heat-transfer liquid) is calculated from an actual volumetric flow of at least one heat-transport liquid and its temperature difference across the heat exchanger. There is a solution US20140222218, where there is a temperature sensor mounted on a primary stream inlet and outlet, and there is a flowmeter measuring flow rate of the primary stream. These sensor data are communicated to a control unit, where an actual absolute power is calculated. The flow rate in this solution is regulated by a motorized valve controlled by the control unit. The disadvantage of this solution is the necessity to use a flow meter to measure the flow rate. The flow meter usage dramatically increases the price of such a device and reduces reliability. This solution uses inlet and outlet primary stream temperature sensors and a flow meter.
The actual volumetric flow rate may also be inferred from an operation conditions of a pump; this solution is described for example in U.S. Pat. No. 8,714,934. The solution uses pump revolutions reading, pump electric power use, and a temperature sensor mounted to a pump motor stator coil to infer the flow rate. These sensor data are communicated to a microprocessor which, using previously stored pump power characteristics, calculates the actual flow rate through the pump. This method had, however, been published before the U.S. Pat. No. 8,714,934 priority date (2 Nov. 2007) in the article Ganapathy, V. “Check pump performance from motor data.” CHEMICAL ENGINEERING 93.19 (1986): 91-92. The referred patent for this solution also does not cover an independent heat flow control.
A system of runtime heat exchanger diagnostics is known, for example, from U.S. Pat. No. 5,615,733. Here the heat exchanger is fitted with temperature sensors on an inlet and outlet of a hot stream, inlet and outlet of a cold stream and there is a flow meter mounted on the hot stream. These sensor data are communicated to a microprocessor, which calculates an overall heat exchange coefficient of the heat exchanger. The calculated heat exchange coefficient is then used to calculate a degree of fouling. A disadvantage of this solution is the need of a flowmeter.
Heat-use measuring is known, for example, from the solution U.S. Pat. No. 4,245,501. Two temperature sensors are attached to an inlet and outlet pipe of a heat exchanger, and there is a flowmeter mounted to this pipe. An analog electronic computation device then calculates an actual heat-use from a temperature difference across the heating terminal and a actual flow rate. A disadvantage of this solution is the need to use a flowmeter. There is also a solution US 2013/0259083 A1, which uses the same temperature measurements as the latter and an ultrasonic flowmeter. Sensor data are communicated to a microprocessor, and the actual heat-use is calculated there. A disadvantage of this solution is the utilization of a flowmeter.